Tomb Raider: The Osiris Codex
Believe it or not, it's more fun to play than the overblown console version.
XIII has a unique and potentially interesting premise, but the game doesn't really differentiate itself from the wide array of other first-person shooters on the market.
Tom Clancy's Rainbow Six 3
The single-player and multiplayer portions of Rainbow Six 3 combine to make this a great game that's easily recommended to Xbox owners looking for a realistic shooter.